Both heparin and non-anticoagulant heparin fragments are known to potentiate angiogenesis in vitro. The purpose of this investigation is to test the ability of heparin and non- anticoagulant heparin fragments to promote intercoronary collaterals in a canine model of myocardial ischemia. In 24 dogs, the origin of the left anterior descending coronary artery (LAD) will be isolated and an ameroid device will be applied to its proximal portion, effecting gradual occlusion over a 2 to 3 week period. Dogs will be randomly assigned to three treatment arms: group 1 will receive heparin; group 2 will receive an equal quantity of non-anticoagulant heparin fragments; and group 3 will receive only 0.9% saline and serve as the control group. Maximal collateral blood flow to the LAD area will be quantitated with microsphere injections during adenosine induced vasodilatation at various times after surgery, so that the time course and maximal extent of collateral growth can be determined and compared in the three groups.